The present invention relates to synthesis of water-dispersible electrically conductive fluorine-containing polyaniline compositions for lithography, and more specifically, to compositions comprising a polymeric acid and copolymers of fluorine-containing anilines for conductive discharge layers.
Polyanilines (PANIs) are some of the most important electrically conductive organic polymers. Water dispersible PANIs have many potential applications including antistatic coatings, conductive paints for corrosion resistance, sensors, and conductive topcoats for electron beam (e-beam) resists. E-beam resists develop a surface potential during exposure that can lead to image placement errors of up to several nanometers, resulting in poor critical dimension (CD) uniformity and image quality. To address this problem, a conductive topcoat, also referred to herein as a conductive discharge layer (CDL), can be used with e-beam resists. The CDL can be removed during subsequent processing steps.
Early conductive PANIs doped with inorganic acids were intractable solids that could not be dispersed in solvents or melted for processing. Subsequently, PANIs doped with small molecule organic acids such as camphor sulfonic acid were found to be dispersible in a limited number of organic solvents such as N-methylpyrrolidine (NMP). Later, water dispersible PANIs were made from aniline monomers by complexing them to polymeric acids such as poly(4-styrenesulfonic acid) and subsequently polymerizing them. This method is described as template-guided polymerization, which is now extensively used to make water dispersible PANIs (U.S. Pat. Nos. 5,370,825, 6,830,708, 7,166,241). In this method, the polymeric acid acts as a template for the polymerization and also as a dopant to the resulting PANI.
Template-guided polymerization of 2-alkyl and 2-alkoxy anilines has been studied extensively. The doped polyanilines of these monomers have greater dispersibility in water than that of the parent unsubstituted aniline polymer, albeit with somewhat lower conductivities. However, these materials do not include water-dispersible fluorine-functionalized polyanilines.
Polymers and co-polymers of 2-fluoroaniline formed by conventional chemical and electrochemical oxidation methods (non-template guided) produce PANIs that are not water-dispersible. Moreover, the polymer molecular weights are low (about 4×103) and the doped polymers, which are not water dispersible, are poorly conducting (10−6 S/cm to 10−3 S/cm) compared to 2 S/cm to 3 S/cm for unsubstituted polyaniline (A. Gok, B. Sari, M. Talu, Synth. Met. 2004, 142, 41 and A. L. Sharma, V. Saxena, V. Annapoorani, B. D. Malhotra, J. Appl. Polym. Sci. 2001, 81, 1460). These observations were attributed to the high electronegativity of fluorine that reduces the electron density of the polymer backbone. However, fluorine-functionalized polyanilines synthesized by a post-polymer modification of unsubstituted polyaniline have high conductivity (0.1 S/cm to 3 S/cm), indicating that the electronegativity of the fluorine group is not solely responsible for the poor conductivity of the conventionally prepared fluorine-containing PANIs (Chien-Chung Han and Hsin-Yu Chen, Macromolecules, 2007, 40, 8969-8973). The probable reason appears to be the sluggish chain propagation reaction of fluorine substituted anilines which results in low molecular weight polymers having poor conductivity.
Therefore, a continuing need exists for water dispersible fluorine-containing PANIs having conductivities suitable for conductive discharge layers (topcoats) used in e-beam lithography.